The overall goal of this project is to develop a new laser desorption time-of-flight (LD/TOF) mass spectrometric technique for the determination of metal isotope ratios that can be readily applied to studies of the metabolism of biologically significant bulk and trace elements.The Phase I goals of this project are to demonstrate the feasibility of an instrument that combines the features of the high accuracy and precision of thermal ionization with the sensitivity, speed, and freedom from memory effects of the LD/TOF instrument. This new instrument should provide broad applicability to metals similar to inductively coupled plasma (ICP) ionization or FAB/SIMS mass spectrometry without the interfering matrix effects. Successful completion of the proposed research will provide a generally applicable mass spectrometric technique for metal tracer studies with better performance than that obtained by thermal ionization, and which is faster and easier to use and requires smaller absolute sample amounts.